1. Field of the Invention
The present invention relates to thin-film magnetic heads, for example, used as floating type magnetic heads and contact type magnetic heads. More particularly, the invention relates to a thin-film magnetic head which is suitable for track width narrowing, and to a method for making the same.
2. Description of the Related Art
FIG. 24 is a partial front view of a conventional thin-film magnetic head 21 viewed from a surface facing a medium (air bearing surface: ABS), and FIG. 25 is a partial sectional view taken along the line XXV—XXV of FIG. 24.
A lower core layer 22 shown in FIGS. 24 and 25 is composed of a soft magnetic alloy, such as an Fe—Ni alloy (Permalloy). An insulating layer (not shown in the drawing) is formed at both sides in the track width direction (in the direction of the X-axis) of the lower core layer 22.
As shown in FIG. 24, a lower pole layer 25, a gap layer 26, and an upper pole layer 27, which constitute a pole section 28, are deposited on the lower core layer 22. The pole section 28 writes information into a medium by a leakage magnetic field from a magnetic gap G with a track width Tw1. As shown in FIG. 25, the pole section 28 extends from a surface 33 facing the medium in the height direction (in the Y direction in the drawing), which may be also referred to as the depth direction of the thin-film magnetic head, to a gap depth (Gd) defining layer (hereinafter referred to as a Gd-defining layer) 23 which will be described below. The lower pole layer 25 and the upper pole layer 27 are composed of a soft magnetic alloy, such as an Fe—Ni alloy (Permalloy), and the gap layer 26 is composed of a nonmagnetic material, such as alumina or an NiP alloy.
The Gd-defining layer 23, which is formed on the lower core layer 22 toward the back from the surface 33 facing the medium, is composed of a nonmagnetic material, such as a resist. As described above, since the pole section 28 extends from the surface 33 facing the medium to the Gd-defining layer 23 in the height direction, a distance from the surface 33 facing the medium to the end of the joint surface between the upper pole layer 27 and the gap layer 26 is defined as the gap depth Gd. As shown in FIG. 25, the Gd-defining layer 23 has a curved surface. In FIG. 24, a broken line indicates the shape of the Gd-defining layer 23 extending from both sides of the pole section 28 in the track width direction.
As shown in FIG. 25, a connecting point lifting layer 29 composed of a soft magnetic alloy, such as an Fe—Ni alloy (Permalloy), is formed on the lower core layer 22 toward the back from the Gd-defining layer 23. As shown in FIGS. 24 and 25, an insulating layer 24 composed of alumina or the like is formed at both sides in the track width direction and at the back in the height direction of the pole section 28, and around the connecting point lifting layer 29. A coil layer 30 is spirally formed on the insulating layer 24, and an insulating layer 31 composed of an organic insulating material or the like is formed so as to cover the coil layer 30.
An upper core layer 32 which is composed of a soft magnetic alloy, such as an Fe—Ni alloy (Permalloy) is, for example, formed by frame plating. A front end 32a of the upper core layer 32 is magnetically coupled to the upper pole layer 27 and is exposed at the surface 33 facing the medium. A base 32b of the upper core layer 32 is magnetically coupled to the lower core layer 22 through the connecting point lifting layer 29. The upper core layer 32 is covered by an insulating layer (not shown in the drawing).
The thin-film magnetic head 21 is, for example, used as a floating type magnetic head, and is built in a magnetic disk unit. When a recording current is applied to the coil layer 30, a recording magnetic field is induced in the upper and lower cores 32 and 22 and also in the upper and lower pole layers 27 and 25 magnetically coupled thereto, and a leakage magnetic field from the magnetic gap G at the surface 33 facing the medium enables writing of information into a magnetic disk which is a magnetic recording medium rotating in the Z direction.
In order to fabricate the thin-film magnetic head 21, first, the Gd-defining layer 23 is formed on the lower core layer 22 at a position receding in the Y direction from the surface 33 facing the medium. Next, as shown in FIG. 26, a resist layer 34 is applied to the lower core layer 22 so as to cover the Gd-defining layer 23, and a recess 34a extending to the Gd-defining layer 23 and a hole corresponding to the connecting point lifting layer 29 are made in the resist layer 34 using photolithography. Additionally, the Gd-defining layer 23 has a curved surface, and each of extending sections 23a and 23b of the Gd-defining layer 23 extending from both sides of the pole section 28 has, for example, a length of approximately 9 μm.
Next, as shown in FIG. 27, a laminate (pole section) 28 is formed by continuously plating the lower pole layer 25, the gap layer 26, and the upper pole layer 27 in the recess 34a using electrolytic plating, and the connecting point lifting layer 29 shown in FIG. 25 is also formed in the hole by electrolytic plating.
As shown in FIG. 31, the insulating layer 24 is then formed on the lower core layer 22 so as to cover the pole section 28 and the connecting point lifting layer 29, and the insulating layer 24 is planarized by performing chemical mechanical polishing (CMP) to the line C—C. Next, as shown in FIG. 32, the coil layer 30 is formed on the planarized insulating layer 24 by combining sputtering, electrolytic plating, and photolithography.
The insulating layer 31 is formed on the insulating layer 24, and the upper core layer 32 is formed on the insulating layer 31 by patterning using frame plating or the like. The fabrication of the major part of the conventional thin-film magnetic head 21 shown in FIGS. 24 and 25 is thereby completed.
In the thin-film magnetic head 21 described above, since the upper pole layer 27 can be formed separately from the upper core layer 32, a narrower track width can be achieved compared to a thin-film magnetic head not provided with an upper pole layer. Since the Gd defining insulation layer is formed, a predetermined gap depth can be defined accurately.
As the density and capacity of the magnetic disk unit are increased, further track narrowing is required in the thin-film magnetic head. The track width Tw1 is determined by the width in the track width direction (in the direction of the X-axis in the drawing) of the gap layer 26. In order to meet the requirement for further gap narrowing, the width of the entire pole section 28 must be decreased. In order to decrease the width of the entire pole section 28, the width T of the recess 34a for forming the pole section 28 must be decreased.
However, if the width T of the recess 34a for forming the pole section 28 is decreased excessively, resolution by photolithography is extremely degraded and the recess 34a cannot be formed with high accuracy. For example, the width T of the recess 34a must be approximately 0.5 μm to allow the accurate formation of the recess 34a by photolithography.
In order to make the track width Tw1 of the pole section 28 smaller than the width which can be obtained with high accuracy by photolithography, a method is known in which after the pole section 28 is formed, the sides of the pole section 28 are physically (or chemically) etched. That is, as shown in FIG. 27, the resist layer 34 is removed after the pole section 28 is formed, and then, as shown in FIG. 28, sides 28a and 28b of the pole section 28 are etched by ion milling or the like in slanting directions (in the A and B directions in the drawing) to decrease the track width Tw1. FIG. 30 shows a state in which both sides of the pole section 28 have been etched.
However, if a decrease of the track width Tw1 to less than 0.4 μm is attempted by etching the sides 28a and 28b using ion milling, the track width Tw1 in the track width direction of the gap layer 26 does not become smallest and, as shown in FIG. 33, the width in the track width direction of the upper pole layer 27 formed on the gap layer 26 becomes smallest. Such a phenomenon is presumed to be caused because the extending sections 23a and 23b of the Gd-defining layer 23 which extend from both sides of the pole layer 28 shadow the lower part of the pole section 28, and irradiated ions do not spread sufficiently to the gap layer 26 and the lower pole layer 25 in the pole section 28. If the width in the track width direction of the upper pole layer 27 is smaller than the width in the track width direction of the gap layer 26, the recording magnetic field guided to the upper pole layer 27 from the upper core layer 32 cannot be concentrated in the magnetic gap G, resulting in a problem in the overwrite characteristic. Magnetic leakage also occurs at the narrowest part of the pole section 28, that is, at the narrowest part of the upper pole layer 27, which may result in write fringing.